1. Field of the Invention
The present invention relates to a semiconductor device having an interface for converting the level of a signal to a voltage level higher than the voltage of its own power supply. More particularly, the present invention relates to a semiconductor device capable of converting the level of a signal to a high voltage level without continuous current consumption.
2. Description of Related Art
Japanese unexamined patent publication No. H10(1998)-22810 discloses an output buffer circuit capable of outputting a signal having a voltage level higher than the voltage of its own power supply. In accordance with the above publication '810, as shown in FIG. 15, the voltage level of an output signal OUT is sequentially amplified from a low voltage level VDD to higher voltage levels (VL1, VH1), (VL2, VH2), (VL3, VH3) and (VL3, VDD2) by using four intermediate inverters operating at power-supply voltages at sequentially increasing voltage levels in order to raise the voltage level of the output signal OUT to a high voltage level VDD2.
The voltage levels VL1 to VL3 and VH1 to VH3 of the power-supply voltages of the intermediate inverters are obtained as a result of applying a voltage division potentiometer comprising resistors 105 to 111 to the high-level voltage VDD2.
In a state where the output buffer circuit disclosed in the publication '810 is capable of outputting the output signal OUT, the voltage levels VL1 to VL3 and VH1 to VH3 of the power-supply voltages to be supplied to the intermediate inverters are obtained as a result of dividing a power-supply voltage VDD2 through the use of a voltage division potentiometer comprising the resistors 105 to 111. Thus, after a transition of a logic level of an input signal IN has been propagated through the intermediate inverters, the logic states of the input/output signals of the intermediate inverters are fixed and, in spite of the fact that no current is consumed in the intermediate inverters, steady current consumption occurs from the power-supply voltage VDD2 through the resistors 105 to 111.
In applications to a technical field of mainly portable devices required to operate at a low current consumption, such steady current consumption raises a problem.
It is thus an object or the present invention, which addresses the problem, to provide a semiconductor device capable of converting the level of a signal to a high voltage level without causing steady current consumption in interfacing a signal between a first circuit group operating at a first power-supply voltage and a second circuit group operating at a second power-supply voltage, which is higher than the first power-supply voltage.